Guidewires have come into widespread use as devices for delivering diagnostic or therapeutic medical devices through body lumens such as a patient's vasculature. In the field of coronary angioplasty, for example, guidewires are generally advanced through a femoral artery access point, through a guiding catheter to reach the ostium of a coronary artery and through the coronary artery to a lesion or clog in the coronary artery. A therapeutic device such as an angioplasty catheter can then be advanced over the guidewire to the lesion. The lesion can be dilated by the angioplasty catheter to improve blood flow through the vessel. To prevent rebound or reclosing of the dilated vessel, a stent can be advanced over the guidewire on a balloon delivery catheter and placed across the dilated lesion.
A typical guidewire for performing angioplasty is at least about 135 cm long. Such a wire generally has a distal tip region extending approximately 7 cm from the distal tip. The distal tip region is generally soft enough to be considered atraumatic. The guidewire typically has an intermediate region extending from about 7 to 35 cm proximally from the distal tip. This region is stiffer than the distal region. The remaining proximal region of the guidewire is usually stiffer yet than the intermediate region.
The intermediate region of the guidewire must be flexible enough to be steerable into a patient's coronary arteries. However, those guidewires having highly flexible intermediate regions are prone to being pulled out or displaced from the coronary arteries when the relatively stiff therapeutic catheters are advanced over them. This is particularly true when a stent and a stent delivery catheter are advanced over such a guidewire.
Conversely, those guidewires having a substantially stiffer intermediate section are not readily steerable into a patient's coronary arteries. When placed, these relatively stiff guidewires tend to straighten curved arteries by placing pressure on the wall of a vessel lumen. When the guidewire is pressed against the wall of the vessel lumen, it becomes more difficult to advance a therapeutic or diagnostic device over the guidewire.